How far should drivers be tested from the Snellen chart?

The correct distance for testing drivers using the Snellen chart is 20 feet. This standard distance is widely used in vision testing as it allows for a consistent and accurate evaluation of visual acuity. At this distance, letters on the chart can be clearly distinguished by an average person with normal vision.

Using the 20-foot measurement ensures that the test results are reliable and comparable to other vision tests that are conducted with the same parameters. Testing at this distance is consistent with DMV and FMCSA guidelines, which require that drivers possess adequate vision to safely operate a vehicle. Moreover, this distance accommodates the size of the letters on the chart, which are designed to be legible at that specific range, thus providing a valid assessment of a driver's visual capabilities necessary for maintaining safety on the road.